1. Field of the Invention
The present invention relates to a projection apparatus and a projection system comprising the same projection apparatus. The present invention especially relates to a projection apparatus that can generate a covering frame on the presenter's body and a projection system comprising the same projection apparatus.
2. Descriptions of the Related Art
Projection apparatuses are commonly used for conveying information in presentations. Examples of such situations include educational and training courses, proposals to potential clients and marketing presentations. However, during these presentations, if the presenter faces the projection apparatus, light rays from the projection apparatus are projected into the user's eyes, causing interference with the user's vision.
A method for matting a signal used in a projector is disclosed in U.S. Pat. No. 6,361,173. According to this method, an infrared light is uniformly irradiated onto a screen to project an image thereon. An infrared sensing video camera then detects and retrieves the signal level of the pixels on the screen. The signal level of the pixels corresponding to a screen area with a clear display is stored and defined as the zero level, and therefore, can be distinguished from the non-zero levels of those pixels in a screen area corresponding to the presenter's shadow. Based on this information, the signal level in the shadow area is then suppressed, thereby, reducing the signal strength projected onto the presenter. However, this method is sensitive to the variation of indoor luminance. For example, if the door or windows are left open or the luminance of lights varies, the projector adapting this method will fail to generate the matte signals.
Another method is disclosed in U.S. Pat. No. 6,789,903, in which a pattern is projected onto a screen by an infrared light projector operating with light at invisible wavelengths. An infrared sensing video camera arranged near the projector detects and stores this pattern to generate a reference frame, which is then transferred to the projector. Subsequently, when the presenter stands in front of the screen, the pattern is projected once again onto the screen by the projector. Similarly, the video camera stores the resulting projection pattern onto the screen, and compares it to the signal obtained from the reference frame to find out the area corresponding to the presenter's shadow. The information is then transferred to the projector, which can suppress image generation in this area according to the information. However, this method requires excessively complex computations, imposing a high burden on the internal processor in the video camera. Moreover, this method further requires a video camera to detect the position of the presenter, which not only makes its operating mechanism more complex, but also increases the cost. Therefore, this method is also not convenient for users.
In summary, the existing methods for improving projection interference are either sensitive to lighting conditions or suffer from excessively complex computations and increased costs. Accordingly, it is still important to provide a projection apparatus that not only prevents the projection image from projecting into the presenter's eye, but is also cost-effective and requires only simple computational mechanisms.